FIELD OF INVENTION
This invention relates to the preparation of hydrofluorocarbons (HFCs). Specifically, it relates to the manufacture of a family of HFCs of the formula: EQU CF.sub.3 (CH.sub.2 CF.sub.2).sub.n F I.
wherein n=1 to 3.
HFCs are of current interest due to their potential to replace ozone depleting CFCs and HCFCs which are used in a variety of applications such refrigerants, propellants, blowing agents, and solvents for degreasing, dewaxing, defluxing, and drying. The compound CF.sub.3 CH.sub.2 CF.sub.2 CH.sub.2 CF.sub.3 (n=2) has physical properties (bp 69.degree.-70.degree. C.) that make it useful as a solvent, and has been (generically) claimed as such in European Patent Application 431 458 A1, published Dec. 6, 1991 (assigned to Daikin Industries) and has also been specifically mentioned as a solvent in U.S. application Ser. No. 746,273 filed Aug. 15, 1991 (assigned to AlliedSignal Inc.). The compound 1,1,1,3,3,3-Hexafluoropropane (n=1) has physical properties (bp -1 C.) which make it attractive a as blowing agent or propellant. It has been claimed as such in EP 381 986 A. The compound CF.sub.3 (CH.sub.2 CF.sub.2).sub.3 F is a novel composition. Its bp of approximately 120.degree. C. makes it a useful compound for e.g., dewaxing and other solvent applications.
There are several literature preparations disclosed for CF.sub.3 CH.sub.2 CF.sub.3 but only one disclosed for CF.sub.3 CH.sub.2 CF.sub.2 CH.sub.2 CF.sub.3. The latter involves the reaction of SF.sub.4 with acetone dicarboxylic acid (HOOCCH.sub.2 C(O)CH.sub.2 COOH) as taught by Bloshchitsa et al., J. Org. Chem. USSR English Translation, 1985, 21, 1414.
Prior art preparations of CF.sub.3 CH.sub.2 CF.sub.3 can be separated into those which involve precursors having no halogens other than fluorine and those which involve the fluorination of chlorinated or brominated precursors. The former type of processes include a) the reaction of SF.sub.4 with propanedicarboxylic acid (J. Am. Chem. Soc., 1960, 82, 543), b) decarboxylation of (CF.sub.3).sub.2 CHCOOH and its salts (Chem. Abstr., 59:15175f), c) from hexafluorothioacetone (Chem. Abstr., 63:483f), and d) the hydrolysis of appropriate precursors including (CF.sub.3).sub.2 CHC(O)C.sub.2 F.sub.5 (Chem. Abstr., 92:180603e) and (CF.sub.3).sub.3 CH (Chem. Abstr. 68:48990d). Processes which involve fluorination of precursors include a) fluorination of hexachloropropene, hexachloropropanes (but not CCl.sub.3 CH.sub.2 CCl.sub.3), or heptachloropropanes with KF (J. Org. Chem., 1963, 28, 112), b) SbF.sub.3 fluorination of BrCF.sub.2 CH.sub.2 CF.sub.2 Br (J. Am. Chem. Soc., 1955, 77, 2783), c) HgF.sub.2 fluorination of CF.sub.3 CH.sub.2 CCl.sub.3 (J. Am. Chem. Soc., 1946, 68, 496), and d) fluorination of hexachloropropene with HF over a catalyst at 400-500 C. which gave CF.sub.3 CHClCF.sub.3 as the main product and CF.sub.3 CH.sub.2 CF.sub.3 also as a product (Chem. Abstr., 115:207499h).
Industry is continuing to search for alternatives to the preparations of CF.sub.3 CH.sub.2 CF.sub.3 cited above, since they may be undesirable for one or more of the following reasons a) the cost of reactants is relatively expensive, b) yields are less than those desired for commercialization, or c) starting are not presently readily available. For example, one process disclosed in the literature for the preparation of CF.sub.3 CH.sub.2 CF.sub.2 CH.sub.2 CF.sub.3 uses a relatively large quantity of SF.sub.4. Because of the cost of SF.sub.4, an alternative process is needed. Accordingly, it is the objective of this invention to provide an economical method for the preparation of telomer compounds of the formula CF.sub.3 (CH.sub.2 CF.sub.2).sub.n=1-3 F using readily available raw materials.